Method for manufacturing stamper for information medium manufacture, stamper, and stamper intermediate with master disk

ABSTRACT

A stamper with a sharp uneven pattern and a favorable surface state is obtained.  
     A photoresist master  100  is manufactured by forming a light absorption layer  103  and a photoresist layer  104,  in that order, on top of a substrate  102,  and then forming an uneven pattern  106  in the photoresist layer  104  by forming and developing a latent image, a Ni thin film  108  is formed on top of the uneven pattern  106  of the photoresist master  100  using either a sputtering method or a vapor deposition method, a Ni film  110  is formed on top of the Ni thin film  108,  and then the Ni thin film  108  and the Ni film  110  are separated from the photoresist master  100  to form a stamper  120.

TECHNICAL FIELD

The present invention relates to a stamper used during the manufactureof an information medium such as an optical disc comprising an unevenpattern such as grooves and prepits, a method of manufacturing thestamper, a stamper intermediate with an attached master formed duringmanufacture, and an information medium manufactured by the stamper.

BACKGROUND ART

Optical discs, which represent one type of information media, arecurrently available in two different varieties: optical recording discswhich enable writing or rewriting of information, and read-only discs inwhich the information has been pre-recorded onto the disc.

A groove (guide channel) that is used for tracking and the like isformed in the disc substrate of an optical recording disc, and arecording layer comprising a phase change material or an organic dyematerial is laminated on top of the disc substrate. When the laser beamis irradiated onto the recording layer, the recording layer undergoes achemical or physical change, thus forming a recording mark. In contrast,in the case of a read-only disc, recording marks (information pits) areformed in advance as part of an uneven pattern on the disc substrate.When a reading laser beam is irradiated onto these recording marks, thequantity of reflected light varies, and by detecting these variations,the information is able to be read (played back).

In order to manufacture a disc substrate with an uneven pattern ofgrooves, information pits, and the like, a stamper is used in which thenegative pattern (which is itself a type of uneven pattern) of thedesired uneven pattern has been formed. For example, a method ofmanufacturing a disc substrate by conducting injection molding using amold with the above stamper secured inside the cavity, therebytransferring the negative pattern to the resin used to fill the cavity,is common.

A stamper with an uneven pattern is usually formed from a metal stampercontaining Ni or the like. In the steps required for manufacturing thisstamper, first a photoresist master with the negative pattern of theuneven pattern of the stamper is prepared, and a metal film is thenformed on this photoresist master by plating. Subsequently, the metalfilm is separated from the photoresist master, and then subjected to aseries of predetermined treatments such as surface washing to form thestamper.

As follows is a description of the manufacturing process for aphotoresist master 1, with reference to the conventional photoresistmaster 1 shown in FIG. 7. First, a photoresist layer 4 is formed on topof a glass substrate 2. Next, the photoresist layer 4 is exposed using apatterning laser beam such as a laser, and the latent image pattern isdeveloped. This enables the production of the photoresist master 1 withan uneven pattern 6 formed in the photoresist layer 4.

In order to use this photoresist master 1 to prepare a stamper 20 byplating, first, as shown in FIG. 8, a thin metal film 8 containing a Nimaterial or the like is formed on the surface of the uneven pattern 6using a process such as electroless plating, thereby impartingconductivity to the photoresist master 1.

Subsequently, electroplating is conducted with the thin metal film 8 asa backing, thereby forming a metal film 10 containing Ni or the like. Byremoving the thin metal film 8 and the metal film 10 from thephotoresist master 1, a stamper 20 containing the transferred unevenpattern 6 can be obtained.

In recent years, as the capacity of optical recording media hasincreased, uneven patterns such as grooves have become much finer,meaning errors in the pattern shape have a large effect on the recordingand reading accuracy. Accordingly, it is desirable to form a sharpuneven pattern on the disc substrate, but in order to achieve this sharppattern, the uneven pattern of the photoresist layer 4, which is thebasis for the pattern, must be formed with a high level of precision(sharpness).

The minimum width of the latent image pattern formed on the photoresistlayer 4 is limited by the spot diameter of the laser beam when itreaches the photoresist layer 4. When λ is the laser wavelength, and NAis the numerical aperture of the objective lens of the irradiatingoptical system, then the spot diameter w is represented by the formulaw=k·λ/NA. k is a constant that is determined by the aperture shape ofthe objective lens and the intensity distribution of the incident lightbeam.

However, even in the case of patterns with widths that theoretically donot exceed the spot diameter limit, if the photoresist layer 4 is thin,then problems of inadequate sharpness can arise due to factors such asshallowness of the uneven pattern transferred to the stamper, orrounding of the shape of the uneven pattern (this is known as patternsag). It is thought that these problems are caused by fluctuationsoccurring in the thickness of the photoresist layer 4 (this is known asfilm thinning) during typical exposure and developing operations. It isthought that these thickness fluctuations are caused by laser beamreflection between the photoresist layer 4 and the glass substrate 2,with this reflection causing excessive exposure of the photoresist layer4.

The inventor of the present invention has clarified that forming a lightabsorption layer between the glass substrate 2 and the photoresist layer4 is an effective way of resolving these problems. By so doing, thelight absorption layer can absorb the laser beam and suppress any lightreflection, and consequently a sharper exposure and development can beachieved than in a conventional process.

However, based on further research, the inventor of the presentinvention noticed that a photoresist master 1 with a light absorptionlayer displayed some problems relating to the formation of the thinmetal film 8 by electroless plating. Specifically, it was surmised thata photoresist master 1 in which the light absorption layer was partiallyexposed was prone to increases in fine irregularities (fine defects)during the electroless plating process. In other words, it wasdiscovered that even though the same method was used to form the thinmetal film, on some occasions when the stamper was removed, for somereason or other fine irregularities (fine defects) had been formed onthe surface of the uneven pattern of the stamper. During playback thesefine irregularities manifest as noise, meaning that despite the attemptto improve the recording capacity by effectively utilizing a lightabsorption layer, in reality a decrease occurs in the recording andplayback performance.

If this problem can be resolved, then the manufacture of a stamper witha sharp uneven pattern should be possible using a photoresist masterwith a light absorption layer.

DISCLOSURE OF THE INVENTION

The present invention is directed to a solution to the above describeddisadvantage, and it is an object of the present invention to provide amethod of manufacturing a stamper in which fine irregularities are notformed on the surface of the uneven pattern on the stamper, as well as astamper manufactured by such a method, a stamper intermediate with anattached photoresist master, and an information medium manufactured bythe stamper.

As a result of intensive research on methods of manufacturinginformation media such as optical discs and magnetic discs (discretemedia), the inventor of the present invention discovered a method offorming a sharp uneven pattern on a stamper while suppressing surfacedefects. In other words, the above object can be achieved by the presentinvention described below.

(1) A method of manufacturing a stamper for manufacturing an informationmedium, comprising the steps of: manufacturing a photoresist master byforming at least a light absorption layer and a photoresist layer, inthat order, on top of a substrate, irradiating light onto saidphotoresist layer from an opposite surface to that which contacts saidlight absorption layer to form a latent image, and then developing saidlatent image to form an uneven pattern; forming a thin metal film on topof said uneven pattern of said photoresist master using either asputtering method or a vapor deposition method; forming a metal film ontop of said thin metal film; and forming the stamper by separating saidthin metal film and said metal film from said photoresist master

(2) A stamper for manufacturing an information medium in a surface ofthe stamper an uneven pattern being formed in advance, the stamper beingmanufactured by the steps of: manufacturing a photoresist master byforming at least a light absorption layer and a photoresist layer, inthat order, on top of a substrate, irradiating light onto saidphotoresist layer from an opposite surface to that which contacts saidlight absorption layer to form a latent image, and then developing saidlatent image to form an uneven pattern; forming a thin metal film on topof said uneven pattern of said photoresist master using either asputtering method or a vapor deposition method; forming a metal film ontop of said thin metal film; and forming the stamper by separating saidthin metal film and said metal film from said photoresist master.

(3) A stamper intermediate with an attached master, in which a thinmetal film is formed on a surface of an uneven pattern of a photoresistmaster for manufacturing a stamper, which has a substrate, a lightabsorption layer laminated on top of said substrate, and a photoresistlayer which is laminated on top of said light absorption layer and iscapable of having an uneven pattern formed therein by forming andsubsequently developing of a latent image, and said thin metal film, onseparation from said photoresist master, forms a part of said stamper,wherein said thin metal film is formed by either a sputtering method ora vapor deposition method.

(4) An information medium, in which a final uneven pattern is formed byusing, as a negative pattern, an uneven pattern of a thin metal film anda metal film of a stamper, the stamper being manufactured by the stepsof: manufacturing a photoresist master by forming at least a lightabsorption layer and a photoresist layer, in that order, on top of asubstrate, irradiating light onto said photoresist layer from anopposite surface to that which contacts said light absorption layer toform a latent image, and then developing said latent image to form anuneven pattern; forming a thin metal film on top of said uneven patternof said photoresist master using either a sputtering method or a vapordeposition method; forming a metal film on top of said thin metal film;and forming said stamper by separating said thin metal film and saidmetal film from said photoresist master.

(5) The information medium according to (4), wherein

-   -   said final uneven pattern is formed by direct transfer of said        uneven pattern from said stamper.        (6) The information medium according to (4), wherein    -   said final uneven pattern is formed by transfer of an uneven        pattern from a mother stamper, and said uneven pattern of said        mother stamper is formed by transfer of said uneven pattern        using said stamper as a master stamper.        (7) The information medium according to (4), wherein    -   said final uneven pattern is formed by transfer of an uneven        pattern from a child stamper, and said uneven pattern of said        child stamper is formed by transfer of an uneven pattern from a        mother stamper, which has been formed by transfer of said uneven        pattern using said stamper as a master stamper.

The inventor of the present invention surmised that it was theapplication of a conventional thin metal film formation process usingelectroless plating to a photoresist master on which a light absorptionlayer had been formed that was causing the generation of fine defects onthe uneven pattern surface, and decided to use a sputtering method or avapor deposition method to form the thin metal film on the photoresistmaster with a light absorption layer.

According to this invention, the quantity of fine defects on the surfaceof the uneven pattern of the stamper can be reduced enormously.Furthermore, with sputtering or vapor deposition, no preliminarytreatment need be conducted on the photoresist master, meaning thestamper manufacturing process itself can be simplified.

Accordingly, the synergistic effect of the advantages offered by thelight absorption layer and the reduction in fine defects provided byusing a sputtering method or a vapor deposition method enables a sharpuneven pattern to be transferred more faithfully to a stamper than byconventional processes. As a result, even as uneven patterns are furtherminiaturized, a compatible surface state can still be retained, and ifthis type of stamper is used, information media such as the grooves andinformation pits of an optical disc can also be formed with goodsharpness, and this makes it possible to improve the recording andplayback characteristics. Furthermore, because the invention iscompatible with future ongoing miniaturization of uneven patterns, italso enables increases in the information memory (recording) capacity ofinformation media.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a photoresist master accordingto an embodiment of the present invention;

FIG. 2(A) is a cross-sectional view showing a state during themanufacture of a stamper using the same photoresist master;

FIG. 2(B) is a cross-sectional view showing the manufactured stamper;

FIG. 3(A) is a diagram showing the result of an AFM analysis of theuneven pattern formed on a stamper according to an example of thepresent invention;

FIG. 3(B) is a line diagram showing the cross-sectional shape of theuneven pattern determined on the basis of the AFM analysis;

FIG. 4(A) is a diagram showing the result of an AFM analysis of theuneven pattern formed on a stamper according to a comparative example ofthe present invention;

FIG. 4(B) is a line diagram showing the cross-sectional shape of theuneven pattern determined on the basis of the AFM analysis;

FIG. 5 is a line diagram showing the uneven state of the stamper surfaceof the above example, as measured by a scanning electron microscope;

FIG. 6 is a line diagram showing the uneven state of the stamper surfaceof the above comparative example, as measured by a scanning electronmicroscope;

FIG. 7 is a cross-sectional view showing a conventional photoresistmaster; and

FIG. 8 is a cross-sectional view showing a state during the manufactureof a stamper using the same conventional photoresist master.

BEST MODE FOR CARRYING OUT THE INVENTION

As follows is a detailed description of an embodiment of the presentinvention, based on the drawings.

FIG. 1 shows a photoresist master 100 according to the embodiment of thepresent invention. This photoresist master 100 comprises a glasssubstrate 102, a light absorption layer 103 laminated on top of thisglass substrate 102, and a photoresist layer 104 laminated on top ofthis light absorption layer 103. A latent image of an uneven pattern isformed on the photoresist layer 104, on the opposite side from the lightabsorption layer 103 (the top side in FIG. 1), by exposure with apatterning laser beam, and development of this latent image causes theremoval of a portion of the photoresist layer, forming an uneven pattern106. Following developing, portions of the light absorption layer 103are exposed at the bottom surfaces of the concave sections of the unevenpattern 106. The numeral 107 in FIG. 1 shows a non-uneven area in whichthe uneven pattern has not been formed.

As described below, the aforementioned uneven pattern 106 becomes thepattern surface 206 of a stamper 120. Furthermore, the area in which theuneven pattern has not been formed becomes the mirror surface 207 of thestamper 120. During exposure, the patterning laser beam is absorbed bythe light absorption layer 103, thereby suppressing light reflection andenabling the formation of fine unevennesses with good sharpness.

FIG. 2(A) shows the stamper 120 formed using the above photoresistmaster 100.

In this formation process, first a sputtering method or a vapordeposition method is used to form a Ni thin film 108 on the surface ofthe uneven pattern 106. At this point, a stamper intermediate 118 withan attached master is obtained, in which the photoresist master 100 andthe Ni thin film 108, which is separated from the photoresist master ina later process and forms a portion of the stamper 120, are integratedtogether as a single unit.

Subsequently, a current is passed through the surface, using the Ni thinfilm 108 as a backing, and electroplating is carried out to form a Nifilm 110. If the Ni thin film 108 and the Ni film 110 are then removedfrom the photoresist master 100, then as shown in FIG. 2(B), a stamper120 comprising an accurately transferred uneven pattern 106 can beobtained.

In this stamper 120, the pattern surface 206 is formed in the areacorresponding with the uneven pattern 106, and the mirror surface 207 isformed in the area corresponding with the non-uneven area 107.

Although not specifically shown in the drawings, the stamper 120 canthen be installed in a mold, and injection molding or the like is usedto manufacture an optical disc substrates having a final uneven patternwhich is created by transferring the uneven pattern 106 as a negativepattern. In addition to using the stamper 120 to manufacture opticaldisc substrates, the stamper 120 can also be used as a master stamperfor preparing a mother stamper by an electroforming process, and thismother stamper can then be used to manufacture optical discs. Inaddition, this mother stamper could also be used as a master forpreparing a child stamper, and this child stamper can then be used tomanufacture the optical discs.

In other words, the stamper 120 of the present invention need notnecessarily be used directly for the manufacture of optical discs, butmay also be used indirectly for such optical disc manufacture, as themaster stamper used in the preparation of a mother stamper or the like.

In the photoresist layer 104 of this embodiment, the provision of thelight absorption layer 103 enables a well defined latent image to beprojected, thus enabling a sharp uneven pattern 106 to be produced. Inaddition, because a sputtering method or a vapor deposition method isused for forming the thin metal film, the Ni thin film 108 can be formedwith an extremely faithful transfer of the state of the uneven pattern106, including any surface defects. Because the uneven pattern 106formed in the photoresist layer 104 contains almost no surface defects,the quantity of fine defects on the surface of the uneven patterntransferred to the stamper 120 can also be significantly reduced. Byusing this stamper 120, information media with suppressed noise levelsand good levels of recording and reading (playback) accuracy can beproduced.

In the present embodiment only the case involving sputtering or vapordeposition using Ni was described, but the present invention is notlimited to this case, and other metals can also be used.

Furthermore, the stamper described above is applicable not only tooptical discs, but can also be applied generally to the manufacture ofinformation media, including magnetic discs (discrete media).

EXAMPLES Example Stamper No. 1

Following formation of a layer of a coupling agent on top of a polishedglass substrate, a light absorption layer was formed by spin coating.The application liquid used was SWK-T5D60 (manufactured by Tokyo OhkaKogyo Co., Ltd.) containing 4,4″-bis(diethylamino)benzophenone as alight absorption agent. The applied layer was baked at 200° C. for 15minutes to cure the layer and remove residual solvent, thus forming alight absorption layer of 140 nm in thickness. Subsequently, aphotoresist (DVR100 manufactured by Zeon Corporation) was spin coatedonto the light absorption layer, and residual solvent was vaporized bybaking, thus forming a photoresist layer of 25 nm in thickness.

Subsequently, using a cutting machine manufactured by Sony Corporation,and targeting the formation of a groove pattern with a track pitch of320 nm and a groove width of 150 nm, the photoresist layer was exposedwith a Kr laser (wavelength=351 nm) and subsequently developed to forman uneven pattern, thus producing a photoresist master.

A Ni thin film was then formed on the surface of the photoresist layerof this photoresist master by sputtering. Electroplating was thenconducted with this Ni thin film as a backing, forming a Ni film. Thelaminate formed from this Ni thin film and the Ni film was separatedfrom the master, the rear surface was polished, and the surface waswashed, thus completing production of a stamper No. 1.

Comparative Example Stamper No. 2

With the exception of forming the Ni thin film using electrolessplating, a stamper No. 2 was prepared in the same manner as thepreparation of the stamper No. 1. Specifically, instead of usingsputtering, the surface of the photoresist layer of the photoresistmaster was activated with a surfactant, and a catalyst (a Pd, Sncolloid) was then applied as a preliminary treatment to electrolessplating. Subsequently, an accelerator (HBF₄ solution) was used to removethe Sn and achieve deposition of the Pd onto the photoresist surface,and the photoresist master was then immersed in a NiCl₂ solution, and aNi thin film was formed by electroless plating.

Comparative Example Stamper No. 3

With the exception of not providing a light absorption layer, a stamperNo. 3 was prepared in the same manner as the preparation of the stamperNo. 1.

Evaluation Results 1

The shape of the uneven pattern formed on each stamper was confirmed byinspection using an AFM (atomic force microscope). A silicon nitride(SiN) probe tip was used for the AFM probe. Measurement was conductedusing a non-contact mode, and the variations in atomic force between thesample and the probe were converted to an image.

FIG. 3(A) shows the AFM image of the stamper No. 1, and FIG. 3(B) is aline diagram showing the cross-sectional shape of the same image.Similarly, FIG. 4(A) shows the AFM image of the stamper No. 3, and FIG.4(B) is a line diagram showing the cross-sectional shape of the sameimage. In the AFM images, the dark areas of high dot density representthe concave sections within the uneven patterns, and the areas of lowdot density or the white areas represent the convex sections, and theseconcave and convex sections correspond with the convex and concavesections respectively of the uneven pattern on the photoresist master.In FIG. 3(B) and FIG. 4(B), the uneven patterns are formed with a pitchof 0.32 μm.

As is evident from comparing FIG. 3 and FIG. 4, in the stamper No. 1that was manufactured in accordance with the present invention, a sharppattern was formed, and that pattern was transferred faithfully to thestamper.

Evaluation Results 2

The uneven states of the stamper No. 1 and the stamper No. 2, asmeasured by a scanning electron microscope (10,000×magnification), areshown in FIG. 5 and FIG. 6, respectively. By comparing FIG. 5 and FIG. 6it is evident that whereas no fine irregularities can be seen for thestamper No. 1, in the stamper No. 2, fine irregularities that appear asindentations with a width of approximately 1 μm are clearly visible atapproximately 3 μm and 8.5 μm along the horizontal axis. In FIG. 5 andFIG. 6, the unevennesses that appear with a pitch of approximately 0.3μm represent the uneven pattern formed in the present invention.

Industrial Applicability

In the present invention, the light absorption layer contacting thephotoresist layer enables the formation of a sharp uneven pattern on thephotoresist master, and by forming a thin metal film by eithersputtering or vapor deposition, fine defects on the pattern surface canbe suppressed while the uneven pattern is transferred faithfully to astamper.

1. A method of manufacturing a stamper for manufacturing an informationmedium, comprising the steps of: manufacturing a photoresist master byforming at least a light absorption layer and a photoresist layer, inthat order, on top of a substrate, irradiating light onto saidphotoresist layer from an opposite surface to that which contacts saidlight absorption layer to form a latent image, and then developing saidlatent image to form an uneven pattern; forming a thin metal film on topof said uneven pattern of said photoresist master using either asputtering method or a vapor deposition method; forming a metal film ontop of said thin metal film; and forming the stamper by separating saidthin metal film and said metal film from said photoresist master
 2. Astamper for manufacturing an information medium in a surface of thestamper an uneven pattern being formed in advance, the stamper beingmanufactured by the steps of: manufacturing a photoresist master byforming at least a light absorption layer and a photoresist layer, inthat order, on top of a substrate, irradiating light onto saidphotoresist layer from an opposite surface to that which contacts saidlight absorption layer to form a latent image, and then developing saidlatent image to form an uneven pattern; forming a thin metal film on topof said uneven pattern of said photoresist master using either asputtering method or a vapor deposition method; forming a metal film ontop of said thin metal film; and forming the stamper by separating saidthin metal film and said metal film from said photoresist master.
 3. Astamper intermediate with an attached master, in which a thin metal filmis formed on a surface of an uneven pattern of a photoresist master formanufacturing a stamper, which has a substrate, a light absorption layerlaminated on top of said substrate, and a photoresist layer which islaminated on top of said light absorption layer and is capable of havingan uneven pattern formed therein by forming and subsequently developingof a latent image, and said thin metal film, on separation from saidphotoresist master, forms a part of said stamper, wherein said thinmetal film is formed by either a sputtering method or a vapor depositionmethod.
 4. An information medium, in which a final uneven pattern isformed by using, as a negative pattern, an uneven pattern of a thinmetal film and a metal film of a stamper, the stamper being manufacturedby the steps of: manufacturing a photoresist master by forming at leasta light absorption layer and a photoresist layer, in that order, on topof a substrate, irradiating light onto said photoresist layer from anopposite surface to that which contacts said light absorption layer toform a latent image, and then developing said latent image to form anuneven pattern; forming a thin metal film on top of said uneven patternof said photoresist master using either a sputtering method or a vapordeposition method; forming a metal film on top of said thin metal film;and forming said stamper by separating said thin metal film and saidmetal film from said photoresist master.
 5. The information mediumaccording to claim 4, wherein said final uneven pattern is formed bydirect transfer of said uneven pattern from said stamper.
 6. Theinformation medium according to claim 4, wherein said final unevenpattern is formed by transfer of an uneven pattern from a motherstamper, and said uneven pattern of said mother stamper is formed bytransfer of said uneven pattern using said stamper as a master stamper.7. The information medium according to claim 4, wherein said finaluneven pattern is formed by transfer of an uneven pattern from a childstamper, and said uneven pattern of said child stamper is formed bytransfer of an uneven pattern from a mother stamper, which has beenformed by transfer of said uneven pattern using said stamper as a masterstamper.